Tanning with alkaline glyoxal



United States Patent TANNING WITH ALKALINE GLYOXAL Ludwig Seligsberger, Newton Center, Mass., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Filed Dec. 23, 1957, Ser. No. 704,846 4 Claims. (Cl. 8-94.33)

(Granted under Title 35, US. Code (1952), see. 266) (CHO.C H .CHO)

at an acid pH, i.e. below pH 7, and preferably between pH 2.5 and 5, to yield a plump and pliable leather.

I have now found, surprisingly, that, apart from formaldehyde (H.CHO), where the fact has been well known, also the dialdehydes glyoxal (CHQCHO) andglutaraldehyde (CHO.C H .CHO), or mixtures thereof, may be used at decidedly alkaline pH, but that smooth grained and pliable leather can only be obtained with any or all of them, when the conditions of the treatment are so adjusted that this decidedly alkaline pH does not cause a swelling eifect. I am aware that it has been attempted heretofore to effect leather tannage with alkaline solutions of formaldehyde followed by washing and drying, but with generally unsatisfactory results, inasmuch as the resulting leather has a damaged grain surface. I ascribe this shortcoming of the prior art to the failure of employing nouswelling alkaline solutions as well as to the omission of an effective neutralization of the tanned hide before washing and drying the same. In other words, satisfactory leather tannage with decidedly alkaline solutions of aldehydes cannot be accomplished if excess alkali is permitted to remain in the tanned hide without chemical neutralization.

I have found that the duration of the tanning treatment in accordance with my invention, including the chemical neutralization step, is substantially shorter than the time consumed by conventional vegetable tanning processes, and yields a full, strong and pliable leather possessing excellent surface characteristics, without grain damage.

In the practice ofmy invention I first immerse the hide in an aqueous alkaline bath until a chemical equilibrium between the bath and the hide has been reached. The strength of concentration of the bath in terms of titratable alkalinity must be in excess of .5 N after equilibrium has been reached; i.e. in a range of about 1 to 2.5 N, and preferably between about 1.5 N and about 2 N, The alkalinity of the bath is etfected in a manner familiar to the industrial chemist, namely by the addition of measured amounts of one or more suitable alkaline chemicals which are compatible with the aldehyde. Ex-

amples of suitable alkaline chemicals are e.g., sodium carbonate, sodium sesquicarbonate (Na CO .NaHCO .2H O) the double salt Na CO .2NaHCO and mixtures of sodium carbonate and sodium bicarbonate and of sod.um carbonate, sodium bicarbonate and sodium hydroxide, also other soluble alkaline salts, such as those of potassium, and alkaline phosphates and silicates. When mixtures of sodium carbonate and sodium bicarbonate are employed in making the concentrated alkaline solutions, it is generally desirable to vary the ratios of sodium carbonate to sodium bicarbonate in terms of molecular proportions from 1:1 to 1:2. The 1:1 ratio is comparable to the use of sodium sesquicarbonate. The 1:2 is comparable to the use of the double salt Na CO .2NaHCO The addit.on of neutral salts to the alkaline liquor is not recommended; however, small amounts of neutral salts that are accidentally present in the alkaline salts used for the pH adjustment, or salts carried from the pickling and bating operations and those which are formed in situ by the neutralization of the pickling acid may be present without detracting from the advantages of the process.

After chemical equilibrium with the hide is thus reached, one or more of the above-named aldehydes is then added to the bath. The pH of the bath, before addition of the aldehyde, must be decidedly on the alkaline side, i.e. should ordinarily be at least about 9.

After tannage is effected by the act.on of the concentrated alkaline solution of the aldehyde, the chemical neutralization of the excess alkali in the tanned hide can be effected by additions of mineral or organic acids, or mixtures thereof, either to the tanning bath, or after draining it off in which latter case sufficient amounts of salts are added, such as NaCl, to prevent swelling, or by the addition of acid salts, such as sodium bisulfate, which prevent any danger of acid swelling, or by the addition of neutral salts which are able to precip.tate carbonates, e.g. Epsom salts (MgSO .7H O). The neutralization step is completed when the tanned hide is stabilized at a neutral or somewhat acid pH (i.e. at a pH of about 7, or less than 7).

If retannage is desired, water soluble tanning agents of a resinous or vegetable type, e.g. quebracho or spruce extracts or synthetic tanning agents (e.g. Syntans or Leukanols) or chrome or aluminum salts, may be employed, and can be added to the acidic neutralizing liquor. However, I do not claim this retanning step as a part of my invention.

After the leather has been stabilized (i.e. has reached chemical equilibrium) and neutralized, as set forth above, it is then dried with or without having been rinsed prior to drying. Retanning may be effected prior to or subse-- quent to drying, if desired.

The herein disclosed aldehydic tanning agents, formaldehyde, glyoxal and glutaraldehyde, may be used either singly or in binary or even ternary mixtures with each other. It is also possible in the practice of my invention to provide a tanning solution of one of the foregoing aldehydes in an alkaline medium, and during the progress of the tannage add another aldehyde; e.g. formaldehyde may be added to a glyoxal tanning bath after the hide has been immersed in the original alkaline bath.

As indicated. the hide may be subjected to conventional pretreatment prior to immersion in the tanning liquor, e.g. pickling and/or bating. However, I have found that the pickling step may be omitted in the practice of my invention (see Example 8) which further accelerates the operation.

The preferred range of alkalinity of the tanning liquor EXAMPLE 1 Tanning with formaldehyde 400 g. of drained pickledcowhide were drummed for two hours with 40 percent of this weight (or 160 cc.) of a solution containing 300 g./l. of soda ash. Then percent based on the pickled weight (or 20 g.) of formaldehyde (minimum concentration: 36 percent) were added in two equal feeds, one hour apart. The drumming continued for six hours. The next day, after drumming for 40 minutes, a shrink temperature of 91 C. was recorded. The tan liquor was then dumped and 50 percent based on the drained pickled weight (or 200 cc.) of a solution containing 50 g./l. of NaCl were added, in which g. of sulfuric acid had also been dissolved. After one hour of drumming, more sulfuric acid, suitably diluted with water to form a solution of 160 g./l., were added in small feeds, 10 or minutes apart, until a pH of 6.5 in the liquor had been attained. The next morning additional small amounts of sulfuric acid were needed to stabilize the pH at 6.2 after a running time of thirty minutes. The tanned hide was washed and dried at 115 F. Bursting strength measurements employing a /s-inch diameter plunger in a modified Scott Ball Burst Tester, in accordance with Provisional Method B 14 of the American Leather Chemists Association (see also reference No. 11), gave approximately 700 lbs./in. on locations with an average thickness of about 10 /2 oz. ,4 inch). The leather was white, supple and free of signs of grain crack.

EXAMPLE 2a Tanning with glyoxal 190 g. of drained pickled cowhide were drummed for one-half hour with 3.8 g. (or 2 percent) of its pickled weight of soda ash dissolved in 142.5 cc. (or 75 percent of drained pickled weight) of water. Then 12 percent more soda ash, in the form of a solution containing 300 g./l. of Na CO was added in three feeds, one-half hour apart. A pH of 10.1 Was reached. 9.5 cc. of a30 percent glyoxal solution, or 5 volume percent of the drained pickled weight of the hide, were now added in two feeds; each was run for one hour. After resting overnight, a shrink temperature of 87 C. was observed. The liquor Was dumped and the hide was neutralized in 95 cc. (or 50 volume percent, based on the drained pickled Weight of the hide), of a 5 percent salt solution, to which 32 cc. of a 2 N acetic acid solution and 77 cc. of a 2 N sulfuric acid solution had been added. After drumming for one-half hour the liquor pH had dropped to 7.2. A number of small feeds of 2 N sulfuric acid solution, added every 15 to 30 minutes, reduced the pH further to 5.3; The last two additions were run one hour each to insure equilibrium. After washing thoroughly, the light brownish hide had a shrink temperature of 86 C. The total quantity of acid needed for neutralization was 6.8% of sulfuric acid and 2% of acetic acid based on the drained pickled weight of the hide.

EXAMPLE 2!:

Glyoxal A pickled steer bend, weighing 10 /2 lbs. was milled 1 /2 hours with 7% sodium bicarbonate dissolved in about 60% water and another 3 hours after adding 9% soda ash, dissolved in about 30% water of 105 F. (40 C.).

d (All percentages in this example are based on the drained pickled weight of the hide.) The next day about 1% more sodium bicarbonate and 1.5% more soda ash were added in dry form, whereupon 10% of a commercial aqueous glyoxal solution (30% by Weight), diluted with approximately its own volume of water, were added in two equal portions, 1 hour apart. After milling for 5 hours, the drum was shut down for the night. On the next day, the shrinkage temperature of the tanned hide was 85 C. Thereupon, 6% sodium bichrornate, diluted with about 6% water, were added and drummingwas continued for 3 hours. After resting in the liquor for a minimum of 16 hours (in this particular case for 64 hours), a solution of 10% sodium metabisulfite in 40% water was added in two equal feeds, each one being milled for 15 minutes. Now 5% sulfuric acid (66 B.), diluted with about 20% water, were added in four feeds, 15 minutes apart. The first feed comprised 2 the other three feeds, each of the acid solution. 15 minutes after the last feed the pH was 5.4. Then 4% formic acid (85% concentration), dissolved in 20% water, were added in 4 feeds, of which the first 3 were run 10 to 15 minutes and the last one for 3 hours. After resting overnight, the pH of the hide was 4.7 and its shrinkage temperature 114 C. After wringing out the excess water, the bend was ready for a vegetable retaning and filling process to be conducted in a conventional manner. The resulting leather had a smooth and strong grain and felt firm and solid.

EXAMPLE 3 Tanning with glutaraldehyda 500 g. of pickled steer bend were drummed for one hour in 35% of its weight water and 5.9% of its weight sodium bicarbonate, and for another one and one-half hours after adding 124 cc. of a 300 g./l. sodium carbonate solution, which is the equivalent of 7.4%, on the drained picked weight, Na CO On the next day drumming was continued for one hour, whereupon the pH was found to be 9.3 and the normality of the solution 1.7. g. or 12%, on the drained pickled weight, of a 25% commercial glutaraldehyde solution were added in three feeds, one hour apart, and drumming was continued for three hours after the last feed. After resting over night a pH of 9.35 and a shrinkage temperature of 84.5 C. were noted. The liquor was dumped and the hide was neutralized by drumming in a bath composed of 15%, on the drained pickled weight, Epsom salts in 150%, on the drained pickled weight, water and of 50 cc. 2-normal sulfuric acid. In intervals of 20 minutes, four more feeds of the same sulfuric acid solution were added. After the last feed, drumming was continued for 100 minutes whereupon a pH of 5.1 was noted. Gradual addithe final neutralization of the aldehyde-tanned hide prior to drying.

EXAMPLE 4 Glyoxal 1,740 g. of drained pickled cowhide were drummed in 1,215 cc. of water in which 124 cc. of sodium bicarbonate had been previously dissolved. One hour later, 157 g. of sodium carbonate in 525 cc. of water were added and tumbling was continued for another two hours.

The normality of the liquor, which at this point was found to be around 1.5, was derived from equimolar proportions of sodium carbonate and sodium bicarbonate,

which, therefore, corresponds to the use of sodium sesqui carbonate (Na CO .NaHCO .2H O). The next day, 7.5 volume percent (based on the drained pickled weight of the cowhide) of 30 percent glyoxal solution was added, in three feeds; the running time after the first feed was 30 minutes, after the second feed, 90 minutes and after the third feed, 5% hours. The shrinkage temperature was then 85 C., and rose to 89.5 C. overnight.

About one-half of the hide was washed at 40 C. for nearly five hours with occasional setting out to assist the removal of salt.

The other half of the hide was drummed in 800 cc. of water, containing 22.5 g. of salt and 30 g. of. sulfuric acid. After two hours and 40 minutes, 15 g. more of sulfuric acid was added. Drumming was continued for three and one-half hours, whereupon the pH of the liquor was 3.8. On the next day, the hide was washed for one hour at 40 C.

Both pieces were hung to dry. The shrinkage temperature of the neutralized piece was 88 C., i.e., 2 degrees higher than that of the washed piece. The bursting strength, as determined in accordance with Provisional Method E 14 of the American Leather Chemists Association using a /s-inch diameter plunger, also differed. It was 985 lbs/in. for the neutralized piece and 848 lbs. for the washed piece, a drop of 14 percent.

The neutralized piece was white and had a smooth grain, while the washed piece was of a light cream color and had a drawn grain.

The following examples illustrate the application of my invention to tanning procedures in commercial-type pilot plant equipment and quantities. The data given in these examples are based on 100 lbs. drained pickled weight of hide.

EXAMPLE 5 Formaldehyde PRETREATMENT (MILLING IN DRUM) The hide is immersed in 4 /2 lbs. soda ash, dissolved in 4 /2 gals. at 32 for 30 minutes. 11 lbs. more soda ash, dissolved in 4 /2 gals. are added at 32 C. and the immersion is continued for 5 /2 hours.

Next morning: pH 9.8-norrnality 1.65.

2% lbs. dry soda ash are finally added, and the immersion is continued for another 30 minutes.

TANNAGE (MILLING CONTINUED) 5 lbs. formaldehyde (36% minimum) are added in two equal feeds; first feed /2 hour, second feed 5 hours. Next morning: pH 9.8 as above-normality 1.9- shrinkage temperature 90 C.

LOTVERING OF pH, AFTER DRAINING OF LIQUOR (MILLING CONTINUED) The tanned hide is neutralized by immersions as follows:

lbs. Epsom salts, 2 lbs. formic acid (85% 10 gals. at 38 C.l5 minutes.

Then: 5 /2 lbs. formic acid diluted to 5 /2 gals. at 43 C., /5 at a time, minutes apart. pH after 5th feed 4.8.

Then: 3% lbs. formic acid diluted to 3 /3 gals. at 43 C., first /3l5 minutes, next /325 minutes, last Aain two feeds, minutes and 40 minutes; pH 4.3.

Piled on truck.

pH of liquors pressed out of hide after 64 hours: 5.5.

EXAMPLE 6 Glyoxal PRETREATMENT (MILLED IN DRUM) 7 lbs. sodium bicarbonate are dissolved in 7 gals. water at 27 C. Running time of hide 1% hours. 9 lbs. soda ash are dissolved in 3 gals. of water at 41 C., and added to the bath. Running time of hide3 hours. Next morning: pH 9.2; normality 1.25.

TANNAGE (MILLING CONTINUED) Glyoxal (30%) and running times: 5 lbs.l hour (first feed) 5 lbs.5 hours (second feed) (each diluted to /2 gal. with water).

Next morning:

pH 8.7 Normality .8 Shrinkage temperature C 85 Glutaraldehyde PRETREATMENT (MILLED IN DRUM) 7 lbs. sodium bicarbonate are dissolved in 7 gals. water. Running time of hide 1 /2 hours. 9.3 lbs. soda ash are dissolved in 3.5 gals. water. Running time of hide 3 hours. Next morning: pH 9.2normality 1.25.

TANNAGE (MILLING CONTINUED) Glutaraldehyde (25%) 12 lbs. Running times:

/2 (first feed) 1 hour. /2 (second feed) 5 hours. Next morning, pH 9.2. Normality 1.08.

Shrinkage temperature, C. 78 (butt); 86 (belly).

LOWERING OF pH, AFTER DRAINING OFF LIQUOR (MILLING CONTINUED) Common salt 6 lbs., formic acid (85%) 1 /3 lbs., dissolved in 20 gals. water; running time 10 minutes. Formic acid (85%) 5 lbs., dissolved in 5 gals. water, added in' 6 feeds; running times (in minutes): 20, 20, 20, 10, 10, 30 pH after last feed 4.7.

Piled on truck for 2 hours until neutralized.

The following example illustrates the tanning of a hide with a combination of glyoxal and formaldehyde in accordance with my invention. A ratio of 7.5 parts of glyoxal to 1 part of formaldehyde was used.

EXAMPLE 8 Limed steer hide was paddled for two hours in 500%, on the white weight (limed weight), of a sodium sesquicarbonate solution which is about 1.8 normal, and rested overnight in the liquor. The next day, the hide 'was transferred to a drum together with sufiicient liquor to maintain an float and 7.5% of a commercial aqueous glyoxal solution (30% by weight), diluted with approximately its own volume of water, were added in four equal portions. The drum was run /2 hour and at rest for /2 hour after the first two feeds, and run a full hour after the last two feeds. 1% (on the white weight) of a commercial aqueous formaldehyde solution was added with the fourth feed. After resting overnight, the hide was fully tanned and had a uniform tan colored cut. Its shrinkage temperature was 88, the pH of the tan liquor was 8.9. Drumming was resumed, with 2%, on the white weight, of concentrated sulfuric acid, diluted with twice its volume of water, being added every ten minutes. After five of these feeds, drumming continued until uniform distribution of the acid throughout the hide was assured. Equilibrium was reached within 1 /2 to 5 hours. The final pH was 3.6, but rose overnight to 3.8. The next day the hide, which has a smooth and strong grain, is:ready for a rocker tannage which can be conducted in a conventional-manner. I

As shown'by the foregoing example, it is even possible in the practice of my invention to omit one or both of the preliminary steps of pickling and bating of the hide, which results in a further simplification of the process and saving of time. bath is capable of performing the functions of a conventional pickle or 'of a bate of the strength commonly employed for sole leather.

As shown by the foregoing general description of my invention, and several illustrative examples of carrying the same into practice, I have shownthat hides can be successfully tanned with certain aldehydes under conditions of high alkalinity, provided that the tanning is followed by su-bstantial neutralization of the tanned leather prior to drying. The tanned leather is characterized by high strength, high shrinkage temperature, excellent ap pearance, and freedom from swelling and cracking.

It will be readily understood from the foregoing description of my invention and of several examples for carrying the same into practice, that various changes may be made therein without departing from the spirit of my invention, which changes are thus demed to be encompassed within the scope of my invention, and I therefore desire to claim my invention broadly, as defined by the appended claims.

I claim:

1. In the production of leather, the process of immersing a hide in an alkaline aqueous salt solution having a pH of about 9 to about 10.5 until chemical equili- Apparently, the strongly alkaline brium between said salt' solution'and said hide'lias been reached, the concentration of said salt solution being about 1'2.5 N, then adding glyoxal to said salt solution, lowering the pH of said hide after tannage has been effected by treating said hide with an acidic liquor prior to rinsing and drying said hide, until said hide is stablized at a pH of not more than about 7, and drying the tanned stabilized hide; whereby a full, strong and pliable leather having a grain structure substantially free from swelling and cracking is obtained.

2. Process according to claim 1, wherein a major amount of glyoxal and a minor amount of formaldehyde are added to said bath.

- 3. Process according to claim 1, wherein said -s alt solution is removed from the tanned hide prior to neutralizing said hide with said acidic liquor.

4. Process according to claim 3, wherein a non-alkaline salt is added to said acidic liquor to prevent swelling of said hide.

References Cited in the file of this patent UNITED STATES PATENTS 2,941,859 Fein et a1 June 2, 1960 OTHER REFERENCES Gustavson: The Chem. of Tanning Processes, Academic Press, N.Y., 1956, pp. 260, 261, 279.

Wilson: The Chem. of Leather Manufacture, 2nd ed., vol. II, Chem. Catalog Co., N.Y., 1929, p. 738.

Progress in Leather Science, 1920-45, Br. Leather Manufacturers Res. Assol, London, 1948, p. 514.

UNITED STATES PATENT OFFICE CERTIFICATION .OF CORRECTION Patent No. 2.9711314 February 14, 1961 Ludwig .SeI i gsberger It is hereby certifiedthat error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 69, for "124 cc." read 124 Q.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents 

1. IN THE PRODUCTION OF LEATHER, THE PROCESS OF IMMERSING A HIDE IN AN ALKALINE AQUEOUS SALT SOLUTION HAVING A PH OF ABOUT 9 TO ABOUT 10.5 UNTIL CHEMICAL EQUILIBRIUM BETWEEN SAID SALT SOLUTION AND SAID HIDE HAS BEEN REACHED, THE CONCENTRATION OF SAID SALT SOLUTION BEING ABOUT 1-2.5 N, THEN ADDING GLYOXAL TO SAID SALT SOLUTION LOWERING THE PH OF SAID HIDE AFTER TANNAGE HAS BEEN EFFECTED BY TREATING SAID HIDE WITH AN ACIDIC LIQUOR PRIOR TO RINSING AND DRYING SAID HIDE, UNTIL SAID HIDE IS STABLIZED AT A PH OF NOT MORE THAN ABOUT 7, AND DRYING THE TANNED STABILIZED HIDE: WHEREBY A FULL, STRONG AND PLIABLE LEATHER HAVING A GRAIN STRUCTURE SUBSTANTIALLY FREE FROM SWELLING AND CRACKING IS OBTAINED. 